standing seam underlayment

Michael Tran
6/3/2012
I am the process of getting quotes for a mechanically sealed standing seam metal roof over an addition of the house we just bought. The roof pitch is 2/12 and does not have an attic but does have soffit venting across the entire length of where the metal roof would go. This addition was built in 1996 and has already had a second roof put on. I want to have the roof done right so hopefully we won't have to worry about it ever again. This portion of the house does experience ice damning. There are 2 sky lights in the center of the room and a chimney at the low side (i.e. rain runs down into the chimney). The quotes that we have gotten have ranged from Ice and Water shielding the whole thing to 30 lbs felt. The companies that recommended Ice and Water shield said they would rather do the whole thing since its more or less like a second roof and we have penetrations. The 30 lbs felt company said that if you do the roof right there is no need for ice and water shield. He also said it would be better for the roof to breath. All thoughts, options and opinions are welcome! Thanks in advance.
Todd Miller
Classic Products, Inc.
6/4/2012
I appreciate the greater breathability of felt though it is still not real breathable. Also, the roof system itself will not be breathable. Frankly, given all you have said, I'd like to see a cold roof constructed over the existing roof -- a chamber that could be vented. This will help with the ice damming issues, and allow you to actually have exhaust vents serviced by the soffit vents. It also might give you the opportunity to increase the pitch of your roof.
Info @windowsonwashington.net
An informed customer is our best customer.
6/4/2012
Asphalt impregnated felt changes vapor permeance with moisture content. It is kind of like a smart breather. Despite that feature, it is completely useless in this application and actually counter intuitive in a roofing application. Regardless of roofing type, your roof should not "Breathe" or be vapor permeable (with the exception of wood shakes for drying). I know this goes against everything that justifies those very expensive underlayments like Deck Armor but this is the truth. The ventilation in this case should be accomplished via soffits and a ridge vent combination. If you are having ice damming issues still, you are doing 1 of 2 things and perhaps a combination of the two: -1 You have too much heat loss. Ice Damming (in an overwhelming majority of the cases) is the result of bulk warm air loss. Fix that first with proper air sealing and and insulation and stop the heat loss -2 Your venting may not be as good as you think. Check this for proper air flow and lack of obstruction. A roof should be able to properly identify these type of things but most cannot. Ice Damming may still happen on a metal roof but should never enter the home and especially not on a mechanically seamed metal roof. This is why you see the that metal apron installed on roofs in the Northern Region.
Michael Tran
6/4/2012
Thank you both for your replies. A lot of stuff to consider... Todd, I don't think that we can install a cold roof as you suggest. The roof of the addition meets the back wall of the house about 3 inches below a window. windowsonwashington.net, we have done some work to remedy the heat loss problem. We've changed the recessed lights to air tight models etc. One of the issues that I see is that there is no ridge to vent from. The high side of the addition's roof meets the house. Is there a type of vent that I could have installed there? I have looked and haven't seen anything. I will check for obstructions to the soffits though. As a side note, the ice damning has never caused a perceivable leak in the house. We have had leaks only during some rain storms which makes me think it is more of a wind driven rain problem. Again any and all thoughts are welcome and appreciated!
Michael Tran
6/4/2012
Thank you both for your replies. A lot of stuff to consider... Todd, I don't think that we can install a cold roof as you suggest. The roof of the addition meets the back wall of the house about 3 inches below a window. windowsonwashington.net, we have done some work to remedy the heat loss problem. We've changed the recessed lights to air tight models etc. One of the issues that I see is that there is no ridge to vent from. The high side of the addition's roof meets the house. Is there a type of vent that I could have installed there? I have looked and haven't seen anything. I will check for obstructions to the soffits though. As a side note, the ice damning has never caused a perceivable leak in the house. We have had leaks only during some rain storms which makes me think it is more of a wind driven rain problem. Again any and all thoughts are welcome and appreciated!
David Neal
Refman
6/4/2012
I am looking to put a standard mental roof over shingles. What type of underlying material should I put down? Felt or something else? thanks
Info @windowsonwashington.net
An informed customer is our best customer.
6/5/2012
You can vent a hip roof but it requires a bit more detail and acknowledgment of water management. If you are putting on Standing seam, you can vent between the ribs of the seam with standard vents or you can just incorporate some sort of vent where the hip roof meets the home.
Todd Miller
Classic Products, Inc.
6/5/2012
David, the underlayment will be as dictated by local building code as well as specifications provided by your roofing manufacturer. Much of the industry has gone toward synthetic underlayments with ice and watershield as required by code. Again, though, you must adhere to manufacturer specifications and building codes.
Info @windowsonwashington.net
An informed customer is our best customer.
6/7/2012
Have you considered what you will save without removal vs. with removal? I am always a big fan of complete stripping of the entire roof to properly address the roof deck and all flashing details. That is me personally but going over top the old shingles is permissible by most manufacturers.
Michael Tran
6/19/2012
Sorry for the slow reply...I've been asking the various companies about their thoughts on the ice damning issue. It seems as though the consensus is the soffits need to be cleared and that should solve the problem since the roof has such a low pitch. So for the underlayment, would ice and water shielding the whole roof be a good idea? Since we have skylights and a chimney there is only about 2 ten foot strips of roof that would not need it. Also, is there a difference between a 16 inch and a 20 inch standing seam panel other than aesthetics? Is one better than the other? Final question, am I correct in preferring 24 gauge as opposed to 28 gauge? Thanks again for all your help.
Info @windowsonwashington.net
An informed customer is our best customer.
6/20/2012
24 is thicker and more sturdy than 28. Panel width is purely a personal preference and does not make one roof better than the other. Soffit venting is certainly a part of the equation but low slope roofs do not convection vent as well as steeper slope roofs. Make sure you air seal and insulate the attic prior to installation of the new roof so that you are keeping the conditioned air and heat inside the home and out of the attic.

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